Resist pattern forming method using anti-reflective layer, resist pattern formed, and method of etching using resist pattern and product formed

ABSTRACT

Disclosed are methods for forming a resist pattern which solve a problem (dimensional precision degradation) caused by halation and interference phenomena due to reflected light from the substrate, and which are fine and have high precision even with substrates having high reflectivity or substrates having a transparent film or substrates with an uneven surface. A first method forms between the substrate and resist film an anti-reflective film whose photoabsorbance of the exposure light is greater on the substrate surface side than on the resist surface side. A second method forms between the substrate and resist film a two-layer anti-reflective film made up of an upper-layer film which is an interference film for the exposure light and a lower-layer film which has higher exposure light absorbance than the upper-layer film and functions as a light shielding film. A third method forms between the substrate and resist film a two-layer anti-reflective film consisting of a lower-layer film that reflects the exposure light and an upper-layer film that is an interference film for the exposure light. A very high anti-reflection effect can be obtained without aspect ratio problems during the process of forming the anti-reflective film and without being influenced by the kind of substrate including those having a transparent film. With these methods, it is possible to form a fine and highly precise resist pattern. These methods can be used to form patterned resist films to etch object films, e.g., in forming microcircuits and/or gates (and word lines) of semiconductor devices.

This application is a Continuation application of application Ser. No.09/440,111, filed Nov. 15, 1999, now U.S. Pat. No. 6,162,588, which is aContinuation application of application Ser. No. 09/285,010,filed Apr.1, 1999, now U.S. Pat. No. 5,985,517, which is a Continuation ofapplication Ser. No. 09/159,786, filed Sep. 24, 1998, now U.S. Pat. No.5,935,765, which is a Continuation of application Ser. No. 09/021,186,filed Feb. 10, 1998, now U.S. Pat. No. 5,846,693, which is aContinuation of application Ser. No. 08/601,361, filed Feb. 16, 1996,now U.S. Pat. No. 5,733,712, the contents of which are incorporatedherein by reference in their entirety.

BACKGROUND OF THE INVENTION

The present invention relates to a method of forming a resist pattern bylithography and an anti-reflective layer used in forming the resistpattern.

An anti-reflection technology, to suppress reflection of exposure lightfrom a substrate, has been known as a peripheral technology oflithography that meets the necessary conditions of dimensional precisionand resolution required of ULSI manufacture. When exposure light isreflected from the substrate, a thin-film interference occurs in aresist film, producing exposure variations in the direction of resistfilm thickness, called standing waves, and pattern dimension variationscalled multiple interferences caused by resist film thicknessvariations. The former degrades the resolution, while the latterdeteriorates the dimensional precision. Halation, which is caused byexposure light being reflected on uneven surfaces of the substrate indiagonal directions and in random directions, poses a problem that areasthat are originally intended to be shielded from exposure are exposed,making it impossible to form a desired pattern. These problems depend onthe intensity of the reflected light from the substrate. The more thereflected light is reduced, the more these problems are mitigated. Forthis reason, growing efforts are being focused on the reduction of thereflected light from the substrate.

The anti-reflection methods may be classified largely into two groups bytheir working principle. One group of methods uses as an anti-reflectivefilm a so-called photoabsorptive film with a strong capability to absorbexposure light, and the second group utilizes light interference toprevent reflection. As a representative for the former, an ARC(Anti-Reflective Coating) method is available, which applies aphotoabsorptive organic film over the substrate before applying aresist. Light that has passed through the resist toward the substrate isabsorbed by this photoabsorptive organic film before being reflected bythe substrate surface, so that the light reflected from the substrateand returning to the resist is mitigated.

Examples of anti-reflective films of the second group include Si andTiN. The anti-reflective film of Si, SiO_(x)N_(y):H,TiN, etc. isdeposited over a metal such as W and Al to such a thickness that thereflected light from the resist/anti-reflective film interface and thereflected light from the anti-reflective film/substrate interface are inopposite phase with each other in order to reduce the reflection.Conventionally, these methods have been employed in reducing thereflection of light.

The ARC method is described in the Proceedings of SPIE, 1991, vol. 1463,pp. 16-29 and in Japan Patent Laid-Open No. 93448/1984. Theanti-reflective film using light interference is described in JapanPatent Laid-Open No. 6540/1984 and 130481/1982, in the Proceedings ofSPIE, 1994, vol.2197, pp.722-732 and in te Technical Digests ofInternational Electron Device Meeting, 1982, pp.399-402.

SUMMARY OF THE INVENTION

Regarding the problems of the conventional anti-reflection technology,explanations are given separately to the anti-reflection technologyusing light interference and to the ARC technology using lightabsorption.

The anti-reflection method using light interference requires thereflectivity of the resist/anti-reflective film interface and thereflectivity of the anti-reflective film/substrate interface to be equalin order to cancel the reflected light from these interfaces. Becausethe reflected light from the resist/anti-reflective film interface andthe reflected light from the anti-reflective film/substrate interfaceneed to be in opposite phase, the thickness of the anti-reflective filmmust be made constant at any location. This is close to impossible torealize on uneven surfaces of the substrate because, as shown in FIG. 2,a thickness 21 of a stepped portion of the anti-reflective film isgreater than that of a thickness 22 of a planar portion. When thesubstrate surface layer is a transparent film such as a silicon oxidefilm, the reflected light from the reflective interface under thesilicon oxide film and the reflected light from theresist/anti-reflective film interface must be set in opposite phase.This requires a precise film thickness control including the siliconoxide film. If the silicon oxide film is used as an inter-layer film onthe uneven surface of the substrate, the film thickness control isimpossible because the thickness of the silicon oxide film variesgreatly depending on locations. In these cases, therefore, satisfactoryanti-reflection cannot be obtained with the light interferenceanti-reflection film. There is another problem that, to make thereflectivities equal, it is necessary to optimize the complex index ofrefraction of the anti-reflective film material according to thesubstrate material (more precisely, the complex-index of refraction ofthe substrate material). That is, the anti-reflection method using lightinterference makes it necessary to change the anti-reflective filmmaterial each time the substrate material is changed. Theanti-reflection method therefore lacks versatility.

Because it deposits a film, the ARC method has the advantages of beingsimple and versatile, that is, it does not depend on the substratematerial. On the other hand, the ARC method has a problem that theanti-reflective film has a large thickness and therefore this method isnot suited for forming a microfine pattern. When there is a step in thesubstrate surface, the thickness 31 (see FIG. 3) of the anti-reflectivefilm 30 over a stepped portion is smaller than the thickness 32 at theside of the stepped portion and the thickness 33 of the planar portion.This makes it necessary to set the thickness over the stepped portiongreater than is required. Further, when performing lithography on aplanar substrate, the anti-reflective film should be formed thick. Toincrease photoabsorbance in the anti-reflective film and at the sametime reduce the film thickness requires increasing the photoabsorbancelevel of the anti-reflective film. As the photoabsorbance levelincreases the reflectivity of the interface between the anti-reflectivefilm and the resist increases, making it impossible to produce asatisfactory reflection prevention effect. For example, when theextinction coefficient of the anti-reflective film, which indicatesphotoabsorption, exceeds 0.5, the interface reflection between theresist and anti-reflective film much increases. Hence, to obtain asufficient reflection prevention effect, the thickness of theanti-reflective film needs to be increased. When a thick anti-reflectivefilm is used, the ratio of film thickness to pattern width, i.e., anaspect ratio, becomes extremely large in microfine patterns, making theanti-reflective film very difficult to process. At the same time, theformed pattern will easily collapse, resulting in a faulty product. Forexample, if a 0.2 μm pattern is to be formed at ±5% precision, thereflectivity of the substrate needs to be kept within 0.23% (energyreflectivity). To achieve this reflectivity requires the thickness ofthe anti-reflective film to be 0.15 μm or greater because of therelationship between the above mentioned photoabsorbance level and theinterface reflection. The aspect ratio for the pattern is 0.75. Finerpatterns require higher dimensional precision and accordingly thereflectivity must be reduced further, forcing the thickness of theanti-reflective film and the aspect ratio to become still larger.

The present invention has been accomplished with a view to overcomingthe above-mentioned problems experienced with conventional technologies.

That is, it is an object of this invention to provide a resist patternforming method and an anti-reflective film used in the method, which canproduce a satisfactory reflection prevention effect even when there arelarge steps in a substrate surface; which can be used widelyirrespective of the substrate material without being affected byreflections from a substrate having a high reflectivity; which canproduce a satisfactory reflection prevention effect even when thethickness of the anti-reflective film cannot be made large due torestrictions on the aspect ratio; and which can form microfine patternswith high dimensional precision.

It is a further object of the present invention to provide a resistpattern including an anti-reflective film, particularly useful in thepreparation of semiconductor devices, especially in the preparation ofmicrofine circuits of ULSI.

It is a still further object of the present invention to provide amethod of etching a substrate (e.g., a layer on a member), especiallyfor etching a substrate having an uneven surface (e.g., a layer on amember having an uneven surface), using a resist pattern including ananti-reflective film, and the product formed.

It is a still further object of the present invention to provide amethod of forming a semiconductor device, especially an ULSI, includingan etching process, e.g., to form a microfine circuit, the etchingprocess using a resist pattern including an anti-reflective film, andthe semiconductor device formed.

To solve the above problems and achieve the above objects, three methodswere invented.

A first method is to form on the substrate to be processed ananti-reflective film whose exposure light absorbance is greater on thesubstrate surface side than on the resist surface side. This methodsolves the above problems and achieves the above objects.

The methods to change the photoabsorbance for exposure light include thefollowing:

(1) After a film with a high photoabsorbance is formed over thesubstrate, the surface of the film is exposed to a liquid or gaschemical to diffuse the chemical into the film to decompose the lightabsorbing component that has reacted with the chemical and thereby tomake the light absorbance distributed.

(2) After the film with a high exposure light absorbance is formed overthe substrate, a mixing layer of the photoabsorbance film and a resistis generated when applying a resist so that the mixing layer has avariation in the photoabsorbance.

(3) The anti-reflective film is formed by CVD (chemical vapordeposition). During the process of forming this film, the condition offilm forming (such as gas composition) is changed to change thephotoabsorbance.

(4) The anti-reflective film is formed by sputtering. During the processof forming this film, the composition of ambient gas is changed tochange the photoabsorbance.

(5) After the substrate is formed with a film containing aphotoabsorptive compound which has a property of being evaporated byheat, the resulting formed film is heat-treated.

(6) The substrate is formed with a film, which has a property ofabsorbing pattern exposure light and also a property of absorbing lightof a certain wavelength (photoabsorption modulation light), reactingwith the photoabsorption modulation light and progressively losing theability to absorb the pattern exposure light. Then, the entire surfaceof the film is irradiated with the photoabsorption modulation light toform an anti-reflective film whose pattern exposure light absorbance issmaller at the surface of the film than at a deep part of the film.

(7) The substrate is formed with a film, which has a property ofabsorbing pattern exposure light and also a property of absorbing lightof a certain wavelength (photoabsorption modulation light), and, whensubjected to heat treatment after being irradiated with thephotoabsorption modulation light, progressively losing the ability toabsorb the pattern exposure light. Then, the entire surface of the filmis irradiated with the photoabsorption modulation light and then bakedto form an anti-reflective film whose pattern exposure light absorbanceis smaller at the surface of the film than at a deep part of the film.

A second method forms a two-layer reflective film consisting of upperand lower layers over the substrate. The upper layer is an interferencefilm for the exposure light, and the lower layer has a higher exposurelight absorbance than the upper layer.

A third method forms a two-layer film consisting of upper and lowerlayers over the substrate, with the upper layer working as aninterference film for the exposure light and the lower layer reflectingthe exposure light. The upper layer may be formed as a single-layer filmor a multi-layer film.

These methods solve the above-mentioned problems and achieve theabove-mentioned objects of the present invention.

The working of the first method is described below.

The reason that increasing the photoabsorbance level of theanti-reflective film does not necessarily result in a decreasedreflectivity is that the reflectivity of the interface between theanti-reflective film and the resist increases as the photoabsorbancelevel of the anti-reflective film rises. Let the complex index ofrefraction of the anti-reflective film and resist be n₁-ik₁ and n₂-ik₂.The intensity of light passing through the anti-reflective filmattenuates by exp(−4πk₁d/λ). Reflected light of((n₁−n₂)²+(k₁−k₂)²)/((n₁+n₂)²+(k₁+k₂)²) is generated at theresist/substrate interface. As the k₁ representing the photoabsorbancelevel increases, the reflection from the interface between theanti-reflective film and the resist increases. Symbol d represents thefilm thickness of the resist and λ represents the wavelength of theexposure light. k₁ and k₂ are also called extinction coefficients forrespective materials.

This invention gradually changes the photoabsorbance of theanti-reflective film beginning with its surface to prevent reflectionfrom the resist/anti-reflective film interface while providing the filmwith a high photoabsorbance level, thus securing a high anti-reflectioneffect. That is, by progressively changing the extinction coefficient kstarting with the resist and ending with the anti-reflective film, thereflection is attenuated. Although a slight reflection is generated eachtime k changes, because the reflection surface shifts slightly at eachchange, the phase of the reflected light changes slightly canceling thebeams of reflected light. As a result, the overall reflection decreases.Because the reflection from the interface is reduced for this reasoneven when the extinction coefficient of the anti-reflective film islarge, a high reflection prevention effect can be produced. Since theextinction coefficient of the anti-reflective film can be increasedwithout a restriction of the interface reflection, the use of thisanti-reflective film assures a satisfactory reflection prevention evenwith a substrate having a high reflectivity or with a substrate whoseupper layer is transparent. Especially when the extinction coefficientk₁ of the anti-reflective film exceeds 0.6, this method has an extremeanti-reflective effect.

The interface reflection prevention utilizes a sort of interferencephenomenon. Because what is utilized for the interference phenomenon isonly a portion of a certain thickness on the upper surface side of theanti-reflective film, a sufficient anti-reflection effect can beobtained even when the film thickness of the anti-reflective filmchanges, as long as it is thicker than a certain thickness. Therefore,the reflection prevention is not influenced by stepped portions in thesubstrate surface.

On the other hand, the conventional anti-reflective film using theinterference phenomenon has the reflected light from theresist/anti-reflective film interface and the reflected light from theanti-reflective film/substrate interface interfere with each other.Hence, when the film thickness of the entire anti-reflective filmchanges, a sufficient reflected light attenuation effect cannot beobtained, leaving the reflection prevention to be greatly influenced bythe stepped portion on the substrate surface. The portion in theanti-reflective film whose light absorbance varies should preferablyhave at least λ/4n_(A), where n_(A) represents an average refractiveindex (real part) of the anti-reflective film within that film thicknessand λ represents the wavelength of the exposure light. It isparticularly desirable that the portion has a thickness equal to an oddnumber times λ/4n_(A). The methods of progressively changing the valueof k along the depth direction include one that continuously changes kand one that changes it stepwise little by little. When the diffusionphenomenon and the mixing phenomenon are utilized, the continuouslychanging method is easier in terms of process.

The methods (6) and (7) described in the foregoing first form over thesubstrate an anti-reflective film, which has a property of absorbing thepattern exposure light and a certain kind of light (referred to asphotoabsorption modulation light), and which, upon reacting with thephotoabsorption modulation light, loses the property of absorbing thepattern exposure light. These methods then irradiate the photoabsorptionmodulation light against the entire surface of the anti-reflective film.The photoabsorption modulation light attenuates in the anti-reflectivefilm according to Lambert-Beer's law and its attenuation distribution inthe direction of propagation of the photoabsorption modulation lightstarts from the surface of the anti-reflective film. At the same time,there is generated a photoabsorption distribution of the patternexposure light beginning with the surface of the anti-reflective film.That is, as indicated by a photoabsorption characteristic curve 51 inFIG. 5—in which the position of the surface of the anti-reflective filmis represented by 0 and the film thickness is represented by d- there isproduced in the anti-reflective film a photoabsorption distribution, inwhich the photoabsorption of the pattern exposure light is weak atposition 0 on the surface of the film and then progressively increasesin the direction of depth. This distribution starts with the surface ofthe film and thus does not change even when the thickness of theanti-reflective film varies according to locations due to the steppedportions in the substrate as shown in FIG. 3. That is, the patternexposure light absorption distribution for the thin film area at the topof the stepped portion (34 of FIG. 3) and that for the thick film areaat the bottom of the stepped portion (35 of FIG. 3) are hardly differentfrom each other, as shown in FIG. 6. The photoabsorption distributionsare equal up to the depth d_(o) to which the photoabsorption modulationlight penetrates, and in deeper areas they exhibit constantphotoabsorptions. Symbols d₁ and d₂ in FIG. 6 represent the positions onthe substrate for the levels 34 and 35, with the surface of theanti-reflective film taken as 0, and have the same values as the filmthicknesses 31 and 32. To describe more precisely, it is not in thedirection of film thickness but in the direction of light propagationthat the photoabsorption distribution does not change. When, forexample, the surface of the anti-reflective film has a slope caused bythe stepped portions of the substrate, the photoabsorption modulationlight 41, as shown in FIG. 4, bends at the surface of theanti-reflective film. In this bent direction the same photoabsorptiondistribution can be obtained. In FIG. 4, reference numeral 42 representsa substrate with a stepped portion; 43 a portion of the anti-reflectivefilm in which the absorption level (extinction coefficient) changes(i.e., there is a gradient in photoabsorption); and 44 a portion of theanti-reflective film that has a constant photoabsorption level. Becausethe pattern exposure light also bends at the interface of theanti-reflective film, a uniform photoabsorption distribution for thepattern exposure light can be obtained, thus reducing reflection withoutbeing influenced by stepped portions.

With this process, the extinction coefficient k can be varied graduallyfrom the resist to the anti-reflective film, thereby reducing thereflection that is caused by rapid change of k. Although a slightreflection is generated each time k changes, because the reflectionsurface is shifted progressively, the phase of the reflected lightchanges little by little, producing a canceling effect. Thus, thereflection as a whole decreases. Because the reflection from aninterface is reduced in this way, a high reflection prevention effectcan be obtained even if the extinction coefficient of theanti-reflective film is large. Since the extinction coefficient of theanti-reflective film can be increased without a restriction of theinterface reflection, the use of this anti-reflective film ensures asatisfactory reflection prevention either with a substrate having a highreflectivity or with a substrate whose upper layer is transparent. Theinterface reflection prevention utilizes a sort of interferencephenomenon. Because what is utilized for the interference phenomenon isonly a portion of a certain thickness on the upper surface side of theanti-reflective film, a sufficient anti-reflection effect can beobtained even when the thickness of the anti-reflective film changes, aslong as it is thicker than the certain thickness. Further, because thethickness used for the interference effect is well controlled in thedirection of light travel, the anti-reflection rate is high. Therefore,the reflection prevention is not influenced by the stepped portions ofthe substrate. On the other hand, the conventional anti-reflective filmusing the interference phenomenon has the reflected light from theresist/anti-reflective film interface and the reflected light from theanti-reflective film/substrate interface interfere with each other.Hence, when the film thickness of the entire anti-reflective filmchanges, a sufficient reflection attenuation effect cannot be obtained,leaving the reflection prevention to be greatly influenced by thestepped portion on the substrate surface. The portion in theanti-reflective film whose light absorbance varies (43 in FIG. 4 andO-d_(o) position range in FIG. 6) should preferably be at leastλ/4n_(A), where n_(A) represents an average refractive index (real part)of the anti-reflective film within that film thickness and λ representsthe wavelength of the exposure light. It is particularly desirable thatthe portion has a thickness equal to an odd number times λ/4n_(A).

The anti-reflective film, which has the property of absorbing thepattern exposure light and, upon reaction with the photoabsorptionmodulation light, loses the property of absorbing the pattern exposurelight, can be produced by diffusing in an organic film a photoabsorptivecompound that becomes transparent as it is exposed to light, a so-calledbleaching characteristic. Alternatively, it may be obtained by using afilm, which has a property of absorbing photoabsorption modulationlight, and, when subjected to heat treatment or chemical treatment afterbeing irradiated with the photoabsorption modulation light, losing theability to absorb the pattern exposure light.

An illustrative (but not limiting) group of compounds having thisbleaching characteristic is the nitrone compounds. These compounds aredescribed in Hamer, et al., Chem. Rev., 64, 472 (1964) at 474, thecontents of which are incorporated herein by reference in theirentirety, and are compounds containing the group:

A specific type of nitrone which can be used in the present invention isset forth in the following:

When this specific type of nitrone is irradiated with light (hv), itreacts to form the following compound (bleached):

The working of the second method is described below.

The lower layer has a high absorbance of exposure light and shieldslight reflected from the substrate. The lower layer therefore offers asatisfactory reflection prevention effect even with a substrate withhigh reflectivity and a substrate having a transparent film. Because theshielding of reflected light from this substrate uses a photoabsorptioneffect, not interference, it does not depend on the material of thesubstrate. Generally, however, the use of a photoabsorptive film that isthin and able to shield well the reflected light from the substrateresults in an increased imaginary part of the refractive index(extinction coefficient) of the anti-reflective film and an increasedreflectivity at the resist/anti-reflective film interface, making itimpossible to produce a good reflection prevention effect. This methodsolves this problem by using the interference film of the upper layer.That is, the reflected light from the resist/upper layer anti-reflectivefilm interface and the reflected light from the upper layeranti-reflective film/lower layer anti-reflective film interface witheach other in such a way that these reflected lights cancel each other(the upper layer film thickness is set so that the phases of thereflected lights are opposite to each other). The combined effect of theinterface reflection reduction by the upper layer anti-reflective filmand the substrate reflection reduction by the lower layeranti-reflective film solves the above problem.

The working of the third method is explained below.

The anti-reflective film of the third method consists of an upper layerfilm and a lower layer film. By reflecting the exposure light by thelower layer film, phase and intensity control of the reflected light canbe achieved. That is, because the reflecting surface is not thesubstrate surface but the lower layer film surface, the reflected lighthas a constant phase and intensity regardless of optical constants ofthe substrate and whether there is a transparent film or not. Thereflected light is cut by the upper layer's interference film. In otherwords, the reflected light from the resist/upper layer anti-reflectivefilm interface and the reflected light from the upper layeranti-reflective film/lower layer anti-reflective film interface are madeto interfere with each other so that they cancel each other (the upperlayer film thickness is set so that the phases of the reflected lightsare opposite). The reason that the reflected light can be cut by theupper layer's interference film is that the phase and intensity of thereflected light can be kept constant. This is achieved by theintroduction of the reflective film. The fact that a reflective film isintroduced in realizing the reflection prevention is a feature of thisaspect of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1(a)-(e) are cross sections illustrating the process of a firstembodiment of this invention.

FIG. 2 is a conceptual diagram showing a problem of a conventional(interference anti-reflection) method.

FIG. 3 is a conceptual diagram showing a problem of a conventional (ARC)method.

FIG. 4 is a conceptual diagram showing the features of ananti-reflective film of this invention.

FIG. 5 is a characteristic diagram showing a photoabsorptioncharacteristic in the anti-reflective film of this invention.

FIG. 6 is a characteristic diagram showing a photoabsorptioncharacteristic in the anti-reflective film of this invention.

FIGS. 7(a)-(e) are cross sections illustrating the process of a secondembodiment of this invention.

FIGS. 8(a)-(f) are cross sections illustrating the process of a thirdembodiment of this invention.

FIGS. 9(a)-(f) are cross sections illustrating the process of a fourthembodiment of this invention.

FIGS. 10(a)-(e) are cross sections illustrating the process of a fifthembodiment of this invention.

FIG. 11 is a photoabsorption characteristic diagram of theanti-reflective film of the third embodiment.

FIGS. 12(a)-(e) are cross sections illustrating a sixth embodiment ofthe invention.

FIG. 13 is a schematic diagram showing the configuration of a projectionand exposure apparatus implementing this invention.

FIGS. 14(a)-(d) are cross sections illustrating the process ofmanufacturing a semiconductor device of this invention.

FIGS. 15(a) and (b) are plan views of major patterns forming thesemiconductor device of this invention.

FIG. 16 is a conceptual diagram showing features of the tenthembodiment.

FIGS. 17(a)-(f) are cross sections illustrating an eleventh embodimentof this invention.

FIG. 18 is a characteristic diagram showing the reflection preventioneffect of the eleventh embodiment.

FIGS. 19(a)-(f) are cross sections illustrating a twelfth embodiment ofthis invention.

FIGS. 20(a)-(g) are cross sections illustrating a thirteenth embodimentof this invention.

FIGS. 21(a)-(f) are cross sections illustrating a sixteenth embodimentof this invention.

FIG. 22 is a characteristic diagram showing the reflection preventioneffect of the sixteenth embodiment.

FIGS. 23(a)-(f) are cross sections illustrating a seventeenth embodimentof this invention.

FIGS. 24(a)-(g) are cross sections illustrating an eighteenth embodimentof this invention.

FIG. 25 is a characteristic diagram showing the reflection preventioneffect of a twentieth embodiment.

And FIGS. 26(a)-(e) are cross sections illustrating a twenty-thirdembodiment of this invention.

DETAILED DESCRIPTION OF THE INVENTION

In the following description, the present invention is described inconnection with specific and preferred embodiments. It will beunderstood that the present invention is not limited to theseembodiments, but rather is to be construed to be of the spirit and scopedefined by the appended claims.

In the present specification, the structure and process are described ascomprising specific components and steps, respectively. It is within thecontemplation of the present inventors that the structure and processcan consist essentially of, or consist of, the disclosed components andsteps, respectively.

Embodiment 1

An embodiment of this invention will be described by referring to FIGS.1(a)-1(e), illustrating the process. First, as shown in FIG. 1(a), anorganic matter 2 containing a nitrone compound was applied over thesubstrate 1 to a thickness of 0.2 μm. Although this figure shows thesubstrate without a step, the substrate may have a step. Next, as shownin FIG. 1(b), the substrate 1 having the organic matter 2 was exposed inan HCl containing gas 3 for 2 minutes. As a result, the HCl gaspenetrated into the organic matter 2 to a depth of about 0.15 μm. Here,the photoabsorbance change reference depth λ/4n_(A) for the interfacereflection prevention is about 0.05 μm for i line radiation (wavelength365 nm), and the depth in this embodiment is about 3 times (odd numbertimes) the reference depth. The n_(A) of the organic matter 2 is about1.65. The nitrone compound in the area in which HCl penetrated underwenta cyclic reaction depending on the concentration of HCl, reducing thephotoabsorbance level for the i line radiation. Because the density ofHCl is high at the surface of the organic matter 2, it was possible toform over the substrate an anti-reflective film for the i lineradiation, whose photoabsorbance is small at the surface of the organicmatter 2 and continuously increases in the direction of depth.

Although in this case HCl gas was used, an HCl solution may be used. Oneof the differences between the two is the penetration depth, with gaspenetrating deep and the HCl solution penetrating only a shallow depth.They can be selected according to the setting of depth. For example, inthe case of an ArF excimer laser exposure light (wavelength 193 nm), amicrofine pattern is required to be formed and the anti-reflective filmneeds to be extremely thin. In such a case, the HCl solution isadvantageous. Then, as shown in FIG. 1(c), a resist 4 was applied andbaked, and then irradiated with an exposure light 6 through a mask 5 inan ordinary manner. Here, the exposure light used an i line radiation.Although the figure shows the mask set close to the substrate duringexposure, it is possible to perform the exposure through a lens, ormirror. Next, as shown in FIG. 1(d), the exposed film was developed toform a resist pattern 4 a in an ordinary way. After this, as shown inFIG. 1(e), with the resist pattern 4 a as a mask, the organic matter 2(anti-reflective film) was etched to form a resist pattern 7 including aprocessed anti-reflective film over the substrate.

The resist pattern formed by this anti-reflection method was about 10%better in the dimensional precision than when a conventionalanti-reflection method was used.

Features of this method include that it is simple in equipmentconfiguration and uses an applied organic film that is easily removed,and that it can control an absorption coefficient variation region bychanging the diffusion length of gas or solution into the organic film,thereby allowing easy application of this method to a variety of kindsof exposure process.

Embodiment 2

A second embodiment of this invention is described by referring to FIGS.7(a)-(e). First, as shown in FIG. 7(a), an organic film 72 was appliedover the substrate and heat-treated at 100° C. The thickness of theapplied film was 0.08 μm over the planar surface. In areas where thefilm is thin due to a step on the substrate, the film thickness was 0.05μm; and in thick areas it was 0.15 μm. The substrate is a silicon wafer70 having an uneven surface or stepped portions, covered with analuminum film 71 (containing 2% silicon) to a thickness of 0.2 μm. Theorganic film used a novolac resin. Although the substrate is shown tohave steps here, it need not be provided with steps.

Next, a shown in FIG. 7(b), a resist 73 was applied over the organicfilm 72. The resist used PMMA (polymethyl methacrylate) and washeat-treated at 200° C. after application. At this time, a mixing layer74 of PMMA and the novolac resin was formed at the interface between theresist 73 and the organic film 72. The thickness of the mixing layer wasabout 0.035 μm, equal to the photoabsorbance change reference depthλ/4n_(A) for preventing interface reflection of ArF excimer laser light.Although the thickness of the organic film 72 varied from one locationto another because of the stepped portions on the substrate, thethickness of this mixing layer was constant.

The surface of the mixing layer on the resist side was PMMA-like and thesurface on the organic film side was novolac-like. The extinctioncoefficient of PMMA for ArF excimer laser light is 0.018, and that ofthe heat-treated novolac resin is about 1. The extinction coefficient ofthe mixing layer was about 0.02 on the upper surface (resist surface)side and about 1 on the lower surface (organic film) side, with theextinction coefficient in between changing continuously. Then, as shownin FIG. 7(c), the resist 73 was irradiated with an exposure light 76through a mask 75 in an ordinary-manner. Here, an ArF excimer laser beamwas used for the exposure light. The organic film 72 and the mixinglayer 74 function as anti-reflective films. While the mask is shownclose to the film, it is possible to perform exposure through a lens ormirror.

Next, the resist 73 was developed to form a resist pattern 73 aaccording to ordinary procedures, as shown in FIG. 7(d). Then, as shownin FIG. 7(e), with the resist pattern 73 a as a mask, the mixing layer74 and the organic film 72 (anti-reflective film) were etched to form aresist pattern 77 including a processed anti-reflective film.

This anti-reflection method was used to form a 0.15-μm pattern, whosedimensional accuracy was 10%. When the ARC anti-reflection method(conventional anti-reflection method) with film thickness of 0.08 μm wasused, the dimensional accuracy was 20% even after the photoabsorptioncoefficient was optimized. Increasing the film thickness of ARC posed aproblem of dimensional shift and collapse of resist pattern duringetching.

Another advantage of the mixing layer is that it works as a bondinglayer making pattern collapse (peeling) unlikely.

The key point of this embodiment is forming the mixing layer. Instead ofPMMA resist, another resist could also be used, as discussed in thefollowing. After the mixing layer is formed, the PMMA resist can beremoved by DUV (deep ultraviolet) irradiation and development. Afterthat, a resist can be spun on the mixing layer and baked in aconventional manner. Then exposure and development is performed.Thereafter, the mixing layer and organic film thereunder are etched toform a resist pattern including a processed anti-reflection film.

Embodiment 3

A third embodiment of this invention is described by referring to FIGS.8(a)-(f). First, as shown in FIG. 8(a), a silicon wafer 80 as asubstrate with steps was deposited with an aluminum film 81 (containing2% silicon) to a thickness of 0.3 μm, and then with a PSG(phospho-silicate glass) film 82. In areas where the PSG film was thindue to steps of the substrate, the film thickness was 0.3 μm; and inthick areas it was 0.6 μm. The PSG film is transparent to a KrF excimerlaser beam (wavelength 248 nm).

Next, as shown in FIG. 8(b), a SiOxNyHz film 83 was deposited over thePSG film by a plasma CVD (chemical vapor deposition) method. TheSiOxNyHz film 83 was formed by using a gas mixture of silane and nitrousoxide and changing the ratio of the mixture during the film forming.Illustratively, the ratio changed from an initial ratio of SiH₄/N₂O of2.9 to a final ratio of 0.1, respectively changing k from 2.0 to 0.02.The thickness of the SiOxNyHz film 83 was set to 0.08 μm. As shown inFIG. 11, the first 0.05 μm (83 a of FIG. 8) was deposited with such agas mixture ratio that the extinction coefficient for the KrF excimerlaser beam was 2. Then, the gas mixture ratio was slowly changed, sothat the extinction coefficient on the resist surface side was 0.02.Because it was a CVD film, the film was able to be formed with a uniformthickness despite the fact that there were steps on the substrate. Theseare advantages of the CVD method.

Next, as shown in FIG. 8(c), the SiOxNyHz film 83 (anti-reflective film)was deposited with a resist 84, which is XP89131 (Shipley: trade name).XP89131 is a chemically amplified resist. A chemically amplified resisthas at least a photo acid generator (PAG). When irradiated, the PAGgenerates acid; and when the irradiated resist is then heated, the acidacts as a catalyst. The extinction coefficient of this resist for a KrFexcimer laser beam is 0.02, equal to the extinction coefficient of thesurface of the SiOxNyHz film 83. Then, as shown in FIG. 8(d), the resist84 is irradiated with exposure light 86 through a mask 85 according to aconventional procedure. A KrF excimer laser beam was used for theexposure light. Though not shown, this exposure used a stepper with alens numerical aperture of 0.45. This is only one example ofexperimental conditions, and a proximity exposure method may be usedinstead.

Then, as shown in FIG. 8(e) the resist 84 was developed to form a resistpattern 84 a according to a conventional procedure. After this, with theresist pattern 84 a as a mask, the SiOxNyHz film 83 was etched to form aresist pattern 87 including a processed anti-reflective film, as shownin FIG. 8(f).

This anti-reflection method was used to form a 0.25-μm pattern, whosedimensional accuracy was found to be 5%. When conventional CVD type andARC type anti-reflective films with 0.08-μm thickness were used, thedimensional accuracy could not be improved from 10%, however much thephotoabsorption coefficient was optimized.

Embodiment 4

A fourth embodiment of this invention is explained by referring to FIGS.9(a)-(f). As shown in FIG. 9(a), a silicon wafer 90 as a substrate withsteps is deposited with a tungsten film 91 to a thickness of 0.2 μm andthen with an SOG (spin on glass) film 92. In areas where the SOG filmwas thin due to steps of the substrate, the film thickness was 0.2 μm;and in thick areas it was 0.5 μm. The SOG film is transparent to a KrFexcimer laser beam (wavelength 248 nm).

Next, as shown in FIG. 9(b), a SiNx film 93 was formed over the SOG filmby a DC sputtering method, with silicon as a target and with a gasmixture of Ar and N₂ forming the ambient gas. The thickness of the SiNxfilm was set to 0.07 μm. The first 0.042 μm (93 a of FIG. 9) wasdeposited with a gas mixture ratio that produced the extinctioncoefficient for the KrF excimer laser beam of 2.8. Then, the gas mixtureratio was gradually changed to deposit the remaining 0.028 μm (93 b ofFIG. 9). Deposition of the remaining 0.028 μm started with theextinction coefficient of 2.8 and ended with 0.02. In changing the gasmixture ratio, N₂ flow was increased. Illustratively, initially, the gaswas solely Ar (i.e., N₂=0%); N₂ flow started and increased such that atthe end N₂=30% by volume (Ar:N₂=7:3). This film is formed by sputtering,so that there is little dust generated in the processing equipment, andthe film produced has few defects. This is an advantage of thesputtering method.

The average refractive index (real part) of the SiNx film was 2.2 forthe. KrF excimer laser beam. Hence, the photoabsorbance change referencedepth λ/4n_(A) for preventing interface reflection of this light wasabout 0.028 μm, almost equal to the film thickness of a portion of theSiNx film in which the extinction coefficient changed.

Next, as shown in FIG. 9(c), the SiNx film 93 (anti-reflective film) wascovered with a resist 94, which is XP89131 (Shipley: trade name). Theextinction coefficient of this resist for KrF excimer laser beam is0.02, equal to the extinction coefficient of the surface of the SiNxfilm.

After this, as shown in FIG. 9(d), the resist 94 is irradiated withexposure light 96 through a mask 95 according to a conventionalprocedure. A KrF excimer laser beam was used for the exposure light.Though not shown, this exposure used a stepper with a lens numericalaperture of 0.45. This is only one example of experimental conditions,and a proximity exposure method may be used instead. Next, as shown inFIG. 9(e), the resist 94 was developed to form a resist pattern 94 aaccording to a conventional procedure. After this, with the resistpattern 94 a as a mask, the SiNx film 93 was etched to form a resistpattern 97 including a processed anti-reflective film, as shown in FIG.9(f).

This anti-reflection method was used to form a 0.25-μm pattern, whosedimensional accuracy was found to be 5%. When conventional CVD type andARC type anti-reflective films with 0.07-μm thickness were used, thedimensional accuracy could not be improved from 10% no matter how muchthe photoabsorption coefficient was optimized.

As seen in Embodiments 3 and 4, changing x and y in SiOxNyHz, and x inSiNx, changes both refractive index (real part) and extinctioncoefficient, with respect to both KrF excimer laser radiation and i lineradiation. The effect of the change in x and y is shown in the followingTables 1 and 2, respectively in connection with SiOxNyHz films formed byCVD and SiNx films formed by sputtering.

TABLE 1 CVD (SiOxNyHz) refractive index composition n k wavelength

KrF (248 nm)

i-line (365 nm)

KrF (248 nm)

i-line (365 nm)

TABLE 2 Sutter (SiNx) refractive index composition n k wavelength

KrF (248 nm) saturation point is ≅ 0.4 (when x ≧ 0.4, n & k ≅ constant)

i-line (365 nm) saturation point is ≅ 0.4

Generally, silicon-rich films have a high extinction coefficient; andwhen z is less than 0.02, the refractive index is relatively insensitiveto a change in z.

Embodiment 5

A fifth embodiment of this invention is explained by referring to FIGS.10(a)-(e). First, as showing FIG. 10(a), a substrate 101 was depositedwith an organic substance 102 to a thickness of 0.1 μm, which forms ananti-reflective film. This organic substance is a novolac resincontaining anthracene as a photoabsorptive compound. Although thisfigure shows the substrate without a step, it may have steps. After theorganic substance 102 was applied, the wafer was subjected to 100° C.heat treatment. The heat treatment evaporates anthracene present nearthe surface of the organic film, generating a distribution of thephotoabsorptive compound. That is, the concentration of thephotoabsorptive compound is high on the substrate side and low on thesurface side.

Next, as shown in FIG. 10(b), the substrate 101 formed with the organicfilm 102 was deposited with a water soluble resist 103. Then, as shownin FIG. 10(c), the resist 103 was irradiated with exposure light 105through a mask 104 according to a conventional process. A KrF excimerlaser beam was used for the exposure light. While the mask is shownclose to the film, it is possible to perform exposure through a lens ormirror. Next, as shown in FIG. 10(d), the resist 103 was developed toform a resist pattern 103 a according to a conventional process. Afterthis, the organic film 102 (anti-reflective film) was etched, with theresist pattern 103 a as a mask, to form a resist pattern 106 including aprocessed anti-reflective film over the substrate.

The resist pattern formed by this anti-reflection method was about 10%better in the dimensional precision than when a conventionalanti-reflection method was used.

Anthracene used as a photoabsorptive compound may be replaced with ananthracene derivative. That is, the substituent group may be changedfrom hydrogen to a methyl group, a methoxy group, an ethyl group orchlorine. Because the volatility changes according to the substituentgroup, it is possible to widen the heat treatment conditions for theorganic film and resist by changing the substituent group.

Features of this method are being able to provide a film-formingapparatus which is simple in equipment configuration, and to produce anoptimum anti-reflective film by a baking furnace.

Embodiment 6

A sixth embodiment of this invention is described by referring to FIGS.12(a)-(e). First, the substrate is deposited with an organic film 112and heat-treated at 100° C., as shown in FIG. 12(a). The film thicknesswas set to 0.1 μm over a planar surface. In areas where the film wasthin due to steps on the substrate surface, the film thickness was 0.06μm. In thick areas, it was 0.18 μm. Because i line irradiation(wavelength 365 nm) was used for the pattern exposure light, thephotoabsorbance change reference depth λ/4 n_(A) for prevention ofinterface reflection was about 0.05 μm, which is thinner than thethickness of the organic film. The organic film 112 used a nitronecompound, a bleaching photoabsorptive compound. As a-substrate, asilicon wafer 110 having steps and deposited with an aluminum film 111(containing 2% silicon) to a thickness of 0.2 μm was used.

Next, as shown in FIG. 12(b), the whole surface of the wafer wasirradiated with i line radiation 113. The flood exposure light(photoabsorption modulation light) 113 transformed a surface portion ofthe organic film 112 into a layer 114, which is transparent at itssurface and which has a photoabsorbance level distribution in which thephotoabsorbance level increases into the layer in the direction of itsthickness. The i line radiation was used for the photoabsorptionmodulation light because of the characteristic of the photoabsorptivecompound used, and the wavelength of the flood exposure light is ofcourse changed if the photoabsorptive compound is changed. The fact thatthe flood exposure light 113 and a pattern exposure light 117 describedlater agreed in wavelength is because of the use of this photoabsorptivecompound. When the photoabsorptive compound is changed, the wavelengthsof the flood exposure light and the pattern exposure light will ofcourse change.

Then, as shown in FIG. 12(c), after a resist 115 was applied to theorganic film 112, exposure light 117 was applied to the resist through amask 116 according to a conventional procedure. An i line radiation wasused for the exposure light as mentioned earlier. While the mask isshown close to the film, it is possible to perform exposure through alens or mirror. The equipment configuration for the latter case is shownin FIG. 13. In the figure, light from a light source 501 illuminates amask 506 through a fly eye lens 502, condenser lenses 503, 505 and amirror 504. A pellicle 507 is provided on the mask 506 to prevent apattern transfer failure due to adhesion of foreign matters. A maskpattern formed on the mask 506 is projected onto a wafer 509, asubstrate to be worked, through a projection lens 508. The mask 506 isplaced on a mask stage 518 whose position is controlled by a maskposition control means 517, and the mask center and the optical axis ofthe projection lens 508 are correctly aligned. The wafer 509 is held ona specimen mount 510 by vacuum suction. The specimen mount 510 is put ona Z stage 511, movable in the direction of the axis of the projectionlens 508, i.e., in a Z direction, and further mounted on an XY stage512. The Z stage 511 and the XY stage 512 are driven by their drivemeans 513, 514, respectively, in response to control commands from amain control system 519, so that the specimen mount 510 can be moved toany desired exposure position. The position of the specimen mount isprecisely monitored by a laser measuring device 515 as a position of amirror 516 fixed to the Z stage 511. The surface position of the wafer509 is measured by a focus position detection means, which comprises adetection beam generator 520, a detection beam 523 and a beam receiver521.

Next, as shown in FIG. 12(d), the resist 115 was developed to form aresist pattern 115 a. Then, as shown in FIG. 12(e), with the resistpattern 115 a as a mask, the organic film 112 (anti-reflective film) wasetched to form over the substrate a resist pattern 118 including aprocessed anti-reflective film. This anti-reflection method was used toform a 0.35 -μm pattern, whose dimensional accuracy was found to be 5%.When a commercially available ARC type anti-reflective film with 0.1-μmthickness was used, the dimensional accuracy was 10%. Increasing thefilm thickness of ARC posed a problem of dimensional shift and collapseof the resist pattern during etching.

Embodiment 7

A seventh embodiment of this invention is described in the following.First, the substrate is deposited with an organic film and heat-treatedat 100° C., as in the sixth embodiment. The thickness of the organicfilm was set to 0.1 μm over a planar surface. In areas where the organicfilm was thin due to steps on the substrate surface, the film thicknesswas 0.06 μm. In thick areas, it was 0.18 μm. Because an h line radiation(wavelength 405 nm) was used for the pattern exposure light, thephotoabsorbance change reference depth λ/4 n_(A) for prevention ofinterface reflection was about 0.06 μm, which is not thicker than thethickness of the organic film. The organic film 112 used a nitronecompound, a bleaching photoabsorptive compound. The substrate used is asilicon wafer stacked successively on its surface with an oxide film 5nm thick, a polysilicon film 0.15 μm thick and an oxide film 0.2 μmthick. The thickness of the oxide films is affected by the steps of thesubstrate and varies from one location to another, as explained inconnection with FIG. 2.

Next, the entire surface was irradiated with an i line radiation. Theflood exposure light (photoabsorption modulation light) transformed asurface portion of the organic film into a layer which is transparent atits surface and which has an photoabsorbance level distribution in whichthe photoabsorbance level increases into the layer in the direction ofits thickness. Then, the wafer was exposed to an acid atmosphere, inthis case, a hydrogen chloride gas. This treatment transformed thenitrone compound into a non-bleaching substance by light irradiation.That is, the photoabsorption modulation light bleached the organic filmto produce a photoabsorbance level distribution, after which thephotoabsorbance level distribution was fixed by exposing the film to theacid atmosphere so that the photoabsorbance level distribution would notchange when subjected to the pattern exposure light at a later process.

Next, after a resist was applied to the organic film, pattern exposurelight was applied to the resist through a mask in a conventional way.The pattern exposure light used a h line radiation as mentioned earlier.

Then, with the resist pattern as a mask, the organic film(anti-reflective film) was etched to form over the substrate a resistpattern including a processed anti-reflective film. This anti-reflectionmethod was used to form a 0.4-μm pattern, whose dimensional accuracy wasfound to be 5%. When a commercially available ARC type anti-reflectivefilm with 0.1-μm thickness was used, the dimensional accuracy was 10%.Increasing the film thickness of ARC posed a problem of dimensionalshift and collapse of the resist pattern during etching.

While this embodiment used a nitrone compound for an organic film, it ispossible to use diazonaphthoquinone instead of the nitrone compound fora photoabsorptive compound, and add a base polymer to form an organicfilm. Alternatively, a mixture of diazonium salt and phenol may be usedfor an organic film, and alkali vapor or ammonia gas may be used for ableaching characteristic fixation gas.

Embodiment 8

An eighth embodiment of this invention is described. First, thesubstrate was deposited with an organic film and heat-treated at 100° C.The thickness of the organic film was set to 0.08 μm over a planarsurface. In areas where the organic film was thin due to steps on thesubstrate surface, the film thickness was 0.05 μm. In thick areas, itwas 0.15 μm. Because a KrF excimer laser beam (wavelength 248 nm) wasused for the pattern exposure light, the photoabsorbance changereference depth λ/4n_(A), for prevention of interface reflection, wasabout 0.035 μm, which is thinner than the thickness of the organic film.The organic film was formed of novolac resin containing indenebisazideas an additive. Other aromatic azides than indenebisazide may be used.The substrate used is a silicon wafer with steps, which is depositedwith an oxide film 10 nm thick, a tungsten polycide film 0.1 μm thickand further an oxide film 0.15 μm thick.

Next, the entire wafer surface was irradiated with light of a wavelengthof 308 nm and then heat-treated at 250° C. Indenebisazide absorbed lightof 308 nm and a distribution of indenebisazide that reacted with thelight was formed beginning with the surface side. Indenebisazide thatdid not react will exhibit a strong photoabsorption characteristic forthe light of 248 nm, when heat-treated later. Therefore, after thelatter heat treatment, a film was formed which strongly absorbs light of248 nm on the bottom side, and, on the surface side, moderately absorbsthis light.

Next, after a resist was deposited on the organic film, the patternexposure light was applied to the resist through a mask in an ordinaryway. As mentioned earlier, the exposure light used a KrF excimer laserbeam. Then, the resist was developed according to a conventionalprocedure to form a resist pattern. With the resist pattern as a maskthe organic film (anti-reflective film) was etched to form over thesubstrate a resist pattern including a processed anti-reflective film.This anti-reflection method was used to form a 0.25-μm pattern, whosedimension accuracy was found to be 5%. When a commercially available ARCtype anti-reflective film with 0.1-μm thickness was used, thedimensional accuracy was 8%. Increasing the film thickness of ARC poseda problem of dimensional shift and collapse of the resist pattern duringetching. This technology was used to form logic LSI gates, whosedimensional precision was found to be 5%. This technology allowedfabrication of high-speed logic LSIs.

Embodiment 9

As a ninth embodiment of this invention, a semiconductor memory deviceis fabricated by using a resist pattern forming method of thisinvention. FIG. 14 is a cross section of a semiconductor memory deviceshowing a major process of manufacture. As shown in FIG. 14(a), a P-typesilicon semiconductor 171 is used as a substrate, on the surface ofwhich is formed a device isolation region 172 by using a known isolationtechnique. Next, word lines 173 are formed which have a laminatedstructure of 150 nm of polysilicon and 200 nm of SiO₂. Further, 150 nmof SiO₂ is deposited by using a chemical vapor deposition method andanisotropically etched to form a side spacer 174 of SiO₂ on the sidewalls of the word line. Next, an n-diffusion layer 175 is formedaccording to a known process. Then, as shown in FIG. 14(b), a data line176 is formed according to a known procedure. The data line is made of apolysilicon or a high melting point metal silicide, or stacked films ofpolysilicon and a high melting point silicide, known in the art. Next,as shown in FIG. 14(c), a SiN film 177 is provided on a side spacer 174on device isolation region 172, and then a storage node 178 ofpolysilicon is formed according to a known procedure. After this, thewafer is deposited with Ta₂O₅, Si₃N₄, SiO₂ or ferroelectric, or acomposite film of these, to form a capacitor insulating film 179. Thisis followed by deposition of polysilicon, high melting point metal, highmelting point metal silicide, or a low resistance conductor such as Aland Cu, to form a plate electrode 180. Next, as shown in FIG. 14(d), aninterconnect 181 is formed according to a known process. Next, the waferis subjected to a known interconnect layer forming process and apassivation process to form a memory device. Only representativemanufacturing processes have been described here. For processes otherthan shown here, known device manufacture techniques are used. If theorder of individual processes differs from what is described above, thisinvention can still be applied. In the above device manufacture, themethod of this invention was employed in almost all processes oflithography. In processes where degradation of dimensional precision dueto reflected light does not pose any problem, for example, thisinvention need not be applied, although it can still be used. Thisinvention was not applied to a via hole forming step in the passivationprocess or to a pattern forming step for making large ion implantationmasks.

Next, our explanation goes to a pattern formed by lithography. FIGS.15(a)-(b) show pattern arrangements in a memory section of arepresentative pattern that forms a memory device. FIG. 15(a) shows oneexample of a pattern of a first device manufactured. Designated 182 areword lines, 183 data lines, 184 active regions, 185 storage nodes, and186 patterns of node leadout holes. This invention was applied to aprocess in the lithography in which precise resolution of microfinepatterns is required. In the pattern of FIG. 15(a), this invention wasapplied to the forming of all patterns.

FIG. 15(b) shows one example of a pattern of a second devicemanufactured. Denoted 187 are word lines, 188 data lines, 189 activeregions, 190 storage nodes, and 191 patterns of node leadout holes. Inthis example, too, this invention was applied to the forming of allpatterns shown here. For the processes other than the pattern-formingprocess shown here that use the minimum design rule, this invention wasapplied.

The characteristic of the device manufactured according to thisinvention was better than those of devices manufactured usingconventional methods. To describe in more concrete terms, variations inthe width of word lines are small and therefore the speed at which datais read out is high and stable. Because variations in area of thestorage nodes are small, data holding characteristics are stable. Thesecharacteristic improvements have been realized. The yield ofsatisfactory products, which was 40% or less in conventional methods, isimproved to as high as more than 70%.

While this embodiment describes the case of a memory LSI, logic LSIshave also realized stabilized and enhanced operation speeds and improvedyield. The greatest reason behind such a significant improvement is animproved controllability of the gate dimension.

Embodiment 10

Before the photoabsorption modulation light was irradiated against theorganic film in the eighth embodiment, the organic film 192 (see FIG.16) was coated with a transparent film 193, which has almost the samerefractive index as the resist and is transparent to the photoabsorptionmodulation light. In this embodiment, polyvinylpyrrolidone was used forthe transparent film. Through this transparent film the photoabsorptionmodulation light 194 was applied to the organic film. After theapplication of this light, the transparent film was removed and thesucceeding processes, from the resist application step forward, similarto those of the eighth embodiment, were carried out to form a resistpattern. Polyvinylpyrrolidone was removed by washing with water. If theorganic film uses a non water-soluble film, this water cleansing willnot cause damage to the organic film, such as degradation and thicknessreduction. Because of this process, the refraction angle θ of thephotoabsorption modulation light at the interface between the coatingfilm 193 and the organic film 192 agrees with the refraction angle ofthe pattern exposure light at the interface between the resist and theorganic film. That is, this process makes it possible to make equal thephotoabsorption distributions in the anti-reflective film in thedirection of pattern exposure light propagation even when the substratestep is large. This in turn permits more precise control of lightinterference in the anti-reflective film, reducing reflection. In thisembodiment, the substrate steps or roughness are made 0.1 μm larger thanthose of the eighth embodiment. Despite the increased surface roughness,the 0.35-μm pattern was able to be formed with an accuracy of 4.5%.

While a transparent coating film was used for the refraction angle θcontrol in this embodiment, it is also possible to use a liquid insteadof a transparent coating film. That is, it is effective to irradiate thephotoabsorption modulation light to the wafer via a liquid, forcontrolling the reflection angle θ. In the case that the refractiveindex of the liquid to the photoabsorption modulation light is close tothe refractive index of the resist to the pattern exposure light, lightinterference in the anti-reflective film can be controlled moreprecisely even when the substrate step is large, because the refractionangle of the photoabsorption modulation light at the interface airbetween the liquid and the organic film agrees with the refraction angleof the pattern exposure light at the interface between the resist andorganic film. The typical liquid is water and oil. The process using theliquid is simple, because the process does not require coating andremoval of the transparent coating film. This is an advantage of theprocess using the liquid.

Embodiment 11

The process of this invention is explained by referring to FIGS.17(a)-(f). First, as shown in FIG. 17(a), a silicon wafer 201 as asubstrate with steps is deposited with a tungsten film 202 to athickness of 0.2 μm and further with an SOG (spin on glass) film 203. Inareas where the thickness of the SOG film is thin due to steps of thesubstrate, the film thickness was 0.2 μm. In thick areas, it was 0.5 μm.The SOG film is transparent to the KrF excimer laser beam (wavelength248 nm).

Next, as shown in FIG. 17(b), the SOG film was deposited with a siliconfilm 204 (light shielding anti-reflective film) to a thickness of 0.025μm by DC sputtering, with Si as a target and Ar as atmosphere.

For the KrF excimer laser beam, the film's refractive index (real part)was 2.3 and extinction coefficient was 2.8. The transmittivity of thisfilm for the KrF excimer laser beam was 3% or lower (energy ratio).Because the reflected light from the substrate travels forward and thenbackward in this film and returns to the resist, the film makes asatisfactory light shielding film.

Then, this silicon film was covered with a SiNx film 205 (interferenceanti-reflective film) to a thickness of 0.025 μm by DC sputtering, withsilicon as a target and with N₂ and Ar as atmosphere. The gas mixtureratio was adjusted so that the refractive index (real part) andextinction coefficient of the SiNx film for the KrF excimer laser beamwere 2.3 and 0.6 respectively.

The film thickness and refractive index are the anti-reflectionconditions for the interference film. This SiNx/Si two-layer film keptthe reflectivity of the KrF excimer laser beam as the exposure lightbelow 0.01% (energy ratio), almost below the nonreflective level,irrespective of the location (i.e., without being influenced by the SOGfilm thickness or steps). Because this two-layer film is formed bysputtering, it does not contain components, such as ammonia, that willdeteriorate the characteristics of a chemically amplified resist. Thiswidens the selection range of resists for use in the two-layercombination of the film. This is an advantage offered by the sputteringmethod.

So far, the Si film forming chamber and the SiNx film forming chamberuse separate sputtering apparatuses. The use of separate chambersenabled a desired gas mixture ratio to be obtained stably. It is alsopossible to form two kinds of film with a single chamber. Common use ofthe chamber of course reduces equipment cost.

Next, as shown in FIG. 17(c), a resist 206 was deposited over the SiNxfilm 205. The resist has a refractive index (real part) of 1.8 andextinction coefficient of 0.02, for the KrF excimer laser beam. Then, asshown in FIG. 17(d), exposure light 208 was applied to the resist 206through a mask 207 according to a conventional procedure. Here, a KrFexcimer laser beam was used for the exposure light. Though not shown,this exposure used a stepper with a lens numerical aperture of 0.45.This is only one example of experimental conditions and a proximityexposure method may be used instead.

Next, as shown in FIG. 17(e), the resist 206 was developed, in aconventional way, to form a resist pattern 206 a. Then, with the resistpattern 206 a as a mask, the SiNx anti-reflective film 205 and thesilicon film 204 were etched to form over the substrate a resist pattern209 including a processed anti-reflective film, as shown in FIG. 17(f).This anti-reflection method was used to form a 0.25-μm pattern, whosedimensional accuracy was found to be 5%. When a conventionalanti-reflective film with 0.05-μm thickness was used, the dimensionalaccuracy could not be improved from 10% no matter how much thephotoabsorption coefficient was optimized. The pattern detection foralignment was done through this anti-reflective film, and a sufficientpattern detection signal was obtained. This is because theanti-reflective film has a sufficient light shielding capability for theKrF excimer laser beam but has a transmittivity of 95% or more for lightwhose wavelength is longer than 540 nm, the wavelength of the patterndetection beam. This is one of the features offered by the SiNx/Sitwo-layer anti-reflective film.

Although this embodiment shows a case of the silicon film thickness of0.025 μm, the silicon film can be equal to or greater than thisthickness. As can be seen from FIG. 22, which shows the change ofreflectivity with the thickness of the SiNx film, a reflectionprevention effect greater than that of the conventional anti-reflectivefilm can be obtained by controlling the thickness of the SiNx film inthe range between 0.017 and 0.039 μm.

Embodiment 12

A twelfth embodiment of this invention is described by referring toFIGS. 19(a)-(f). First, as shown in FIG. 19(a), a silicon wafer 221 as asubstrate with steps was deposited with an aluminum film 222 (containing2% silicon) to a thickness of 0.3 μm, and then with a PSG(phospho-silicate glass) film 223. In areas where the PSG film was thindue to steps of the substrate, the film thickness was 0.3 μm; and inthick areas it was 0.6 μm. The PSG film is transparent to a KrF excimerlaser beam.

Next, as shown in FIG. 19(b), a SiOxNyHz film 224 was deposited over thePSG film by a plasma CVD method. The SiOxNyHz film was formed by using agas mixture of silane and nitrous oxide, with the mixture ratio so setthat the extinction coefficient for the KrF excimer laser beam was 1.8.The refractive index (real part) at this time was 2.2. The filmthickness was set to 0.025 μm. The transmittivity of this film for theKrF excimer beam was 10% or less (energy ratio). Because the reflectedlight from the substrate passes through this film forward and thenbackward before returning to the resist, the film makes a satisfactorylight shielding film.

Then, the light shielding film 224 was deposited with a SiOxNyHz film225 to a thickness of 0.027 μm by the plasma CVD method. As with thefilm 224, the SiOxNyHz film 225 uses a gas mixture of silane and nitrousoxide, but with the mixture ratio so set this time that the extinctioncoefficient for the KrF excimer laser beam was 0.7. The refractive index(real part) at this time was 2.1. Because this is a CVD film, the filmcan be deposited to a uniform thickness despite there being steps on thesubstrate, and thus has high film thickness controllability. This is anadvantage of the CVD method.

This two-layer reflection film consisting of the films 224 and 225 keptthe reflective index of the KrF excimer beam below 0.02% (energy ratio),almost below the nonreflective level, irrespective of the location.

Next, as shown in FIG. 19(c), the SiOxNyHz film 225 was covered with aresist 226, whose refractive index and extinction coefficient for a KrFexcimer laser beam were 1.8 and 0.02 respectively. Then exposure light228 was radiated against the resist 226 through a mask 227 in aconventional way, as shown in FIG. 19(d). The exposure light used a KrFexcimer laser beam. Though not shown, this exposure used a a stepperwith a lens numerical aperture of 0.45. This is only one example ofexperimental conditions, and a proximity exposure method may be usedinstead.

Then, as shown in FIG. 19(e), the resist 226 was developed in aconventional ordinary way to form a resist pattern 226 a. Then, as shownin FIG. 19(f), with the resist pattern 226 a as a mask, the SiOxNyHzanti-reflective films 224, 225 were etched to form over the substrate aresist pattern 229 including processed anti-reflective films.

This anti-reflection method was used to form a 0.25-μm pattern, whosedimensional accuracy was found to be 5%. When a conventional CVD typeanti-reflective film with 0.052-μm thickness was used, the dimensionalaccuracy could not be improved from 10% no matter how much thephotoabsorption coefficient was optimized.

Embodiment 13

Now, by referring to FIGS. 20(a)-(g), a thirteenth embodiment of thisinvention is described. As shown in FIG. 20(a), a silicon wafer 231 wasdeposited with an oxide film 232 (gate oxide film) to a thickness of 4.5nm, and further with a polysilicon film 233 to a thickness of 0.3 μm.The polysilicon film was diffused with phosphorus to make thepolysilicon a conductive film. The polysilicon conductive film was thendeposited with an HLD (high temperature low pressure composition) film234 to a thickness of 0.2 μm. The HLD film was formed at a temperatureof 750° C. and at a pressure of 1.5 torr, using a forming gas of (20%silane (SiH₄)+80% He), 100 sccm, and N₂O, 1300 sccm. Throughout thepresent disclosure, the HLD film can be, e.g., a silicon oxide film,that, for example, is rich in carbon.

Then, as shown in FIG. 20(b), a silicon film 235 (light shielding film)was deposited over the HLD film 234 to a thickness of 0.025 μm by DCsputtering, with silicon as a target and with Ar as the atmosphere. Forthe KrF excimer laser beam, this film has a refractive index of 2.3 andthe extinction coefficient of 2.8. As with the first embodiment, thisfilm has a transmittivity for the KrF excimer laser beam of 3% or less(energy ratio). Because the reflected light from the substrate passesthrough this film forward and then backward before returning to theresist, the film makes a satisfactory light shielding film. This siliconfilm working as a light shielding film may have a greater thickness.

Then, an SiNx film 236 (interference anti-reflective film) was depositedover the silicon film 235 by the DC sputtering method, with silicon as atarget and N₂ and Ar gases as the atmosphere. As with Embodiment 11, thegas mixture ratio was adjusted so that the refractive index (real part)and extinction coefficient of the SiNx film for the KrF excimer laserbeam were 2.3 and 0.6 respectively. A resist 237 was then applied overthe SiNx film 236. For the KrF excimer laser beam, the resist 237 has arefractive index (real part) of 1.8 and an extinction coefficient of0.02.

Next, as shown in FIG. 20(c), exposure light 239 was radiated againstthe resist 237 through a mask 238 in a conventional way. Here, theexposure light used a KrF excimer laser beam. Though not shown, thisexposure used a stepper with a lens numerical aperture of 0.45. This isonly one example of experimental conditions, and a proximity exposuremethod may be used instead.

Next, the resist 237 was developed in a conventional way to form aresist pattern 237 a, as shown in FIG. 20(d). Then, as shown in FIG.20(e), with the resist pattern 237 a as a mask, the SiNx anti-reflectivefilm 236, silicon film 235 and HLD film 234 were etched to form an SiNxpattern 236 a, an Si pattern 235 a and an HLD pattern 234 a. Then, asshown in FIG. 20(f), the resist pattern 237 a was removed in aconventional manner.

After this, as shown in FIG. 20(g), with the SiNx pattern 236 a, Sipattern 235 a and HLD pattern 234 a as a mask, the polysilicon film 233was etched to form a gate interconnect pattern 233 a. At this time, theSi film 235 a and SiNx film 236 a that are thin and whose etch rates arelittle different from that of the polysilicon were removed at the sametime during this etching process. The fact that the anti-reflective filmcan be removed without any special removing process is one of thefeatures of this method. This feature can be obtained not only when thepolysilicon gate interconnect film is used but also when a tungstensilicide film, a tungsten polycide film or a stack of these filmsincluding polysilicon is used.

This anti-reflection method was used to form a 0.25-μm-wide gateinterconnect pattern and its dimensional accuracy was found to be 5%.When a conventional anti-reflective film with 0.05-μm thickness wasused, the dimensional accuracy could not be improved from 10% no matterhow much the photoabsorption coefficient was optimized.

Embodiment 14

As in the case of Embodiment 11, a silicon wafer as a substrate withsteps was deposited with a tungsten film to a thickness of 0.2 μm, andfurther with an SOG (spin on glass) film. In areas where the SOG filmwas thin due to steps of the substrate, the film thickness was 0.2 μm;and in thick areas it was 0.5 μm. The SOG film is transparent to a iline radiation (wavelength 365 nm).

Next, the SOG film was deposited with a silicon film (light shieldinganti-reflective film) to a thickness of 0.025 μm by a DC sputteringmethod, with Si as a target and Ar gas as atmosphere. The film'srefractive index (real part) and extinction coefficient for the i lineradiation was 4.6 and 2.7 respectively. Because the transmittivity ofthe SOG film for the i line radiation is less than 10% (energy ratio)and the reflected light from the substrate passes this film forward andthen backward before returning to the resist, this film makes a goodlight shielding film.

Then, an SiNx film (interference anti-reflective film) was formed overthe silicon film to a thickness of 0.029 μm by a DC sputtering method,with silicon as a target and N₂ and Ar gases as atmosphere. The gasmixture ratio was so set that the SiNx film's refractive index (realpart) and extinction coefficient for the i line radiation would be 2.8and 0.4 respectively. The gas mixture ratio (volume) was Ar/N₂=88:12.These film thickness and refractive index constitute the anti-reflectionconditions of the interference film. This SiNx/Si two-layer film keptthe reflectivity of i line radiation (as the exposure light) below 0.2%(energy ratio), almost below the nonreflective level, irrespective ofthe location (i.e., without being influenced by SOG film thickness orsubstrate steps).

Next, a resist was applied over the SiNx film. The resist's refractiveindex (real part) and extinction coefficient for i line radiation were1.7 and 0.00 respectively. Exposure light was then radiated against theresist through a mask in an ordinary way. An i line radiation was usedfor the exposure light. Next, the resist was developed in a conventionalway to form a resist pattern.

After this, with the resist pattern as a mask, the SiNx anti-reflectivefilm and the silicon film were etched to form over the substrate aresist pattern including a processed anti-reflective film.

This anti-reflection method was used to form a 0.35-μm pattern and itsdimensional accuracy was found to be 5%. When a conventionalanti-reflective film with 0.05-μm thickness was used, the dimensionalaccuracy could not be improved from 15% no matter how much thephotoabsorption coefficient was optimized. Although we described a caseof 0.029-μm thickness, if the thickness of the SiNx film were able to beincreased to 0.1 μm, the reflectivity was further reduced to 0.1% bysetting its refractive index to 2.6 and extinction coefficient to 0.2.

Embodiment 15

A silicon wafer as a substrate with steps was deposited with a tungstenfilm to a thickness of 0.2 μm and further with an HLD film to athickness of 1 μm. Then, its surface was polished planar by CMP(chemical mechanical polishing). Although the surface was made planar,the thickness of the HLD film varied from one location to another due tothe steps of the substrate, ranging from 0.5 μm to 0.75 μm. The HLD filmis transparent to i line radiation (wavelength 365 nm).

Next, with silicon as a target and Ar gas as atmosphere, a silicon film(light shielding anti-reflective film) was formed over the HLD film to athickness of 0.025 μm by a DC sputtering method. This film's refractiveindex (real part) and extinction coefficient for i line radiation were4.6 and 2.7 respectively. Because the transmittivity of the silicon filmfor i line radiation is less than 10% (energy ratio), and the reflectedlight from the substrate passes this film forward and then backwardbefore returning to the resist, this silicon film makes a good lightshielding film.

Then, the silicon film was coated with BARL-i (trade name of an ARC filmfrom Hoechst Co.) to a thickness of 0.06 μm and subjected to an ordinaryheat treatment. The extinction coefficient of this BARL-i film for iline radiation was 0.41. The extinction coefficient of the upper-layeranti-reflective film is smaller than that of the lower-layeranti-reflective film. This BARL-i/Si two-layer film kept thereflectivity of i line radiation (as the exposure light) below 1%(energy ratio), almost below the nonreflective level, irrespective ofthe location.

Next, a resist was applied over the BARL-i film. The resist's refractiveindex (real part) and extinction coefficient for i line radiation were1.7 and 0.00 respectively. Then, the resist was irradiated with exposurelight through a mask in a normal way. Here, i line radiation was used asthe exposure light. The resist was then developed in a conventionalmanner to form a resist pattern. With the resist pattern as a mask, theBARL-i film and the silicon film were etched to form over the substratea resist pattern including processed anti-reflective films.

This anti-reflection method was used to form a 0.4-μm pattern and itsdimensional accuracy was found to be 5%. With only the BARL-i film 0.06μm thick, however, the reflectivity of the anti-reflective film was 16%.And the silicon film with a thickness of 0.025 μm alone could onlyreduce the reflectivity of the anti-reflective film to 40%. That is, theconventional single-layer anti-reflective film could not produce such areflection prevention effect as this example. With the two-layeranti-reflective film, even when the thickness of the BARL-i film wasfurther reduced to 0.04 μm, the reflectivity was below 10%.

Embodiment 16

A sixteenth embodiment of this invention is explained by referring toFIGS. 21(a)-(f). As shown in FIG. 21(a), a silicon wafer 311 as asubstrate with steps was deposited with a tungsten film 312 to athickness of 0.2 mm and further with an SOG (spin on glass) film 313.The thickness of the SOG film varied from one location to another due tothe steps of the substrate, ranging from 0.2 μm to 0.5 μm. The SOG filmis transparent to a KrF excimer laser beam (wavelength 248 nm).

Next, as shown in FIG. 21(b), the SOG film was deposited with a siliconfilm 314 (reflective film) to a thickness of 0.025 μm by a DC sputteringmethod, with Si as a target and Ar gas as atmosphere. Although the gasmixture in this example used Ar and N₂, other inert gases such as Xe andKr may be used. The film's refractive index (real part) and extinctioncoefficient for the KrF excimer laser beam were 2.3 and 2.8respectively. This film reflects the KrF excimer laser beam by more than97% (energy ratio). Then, with silicon as a target and N₂ and Ar gasesas atmosphere, an SiNx film 315 (interference anti-reflective film) wasdeposited over the silicon film to a thickness of 0.025 μm by a DCsputtering method.

The gas mixture ratio was adjusted so that the SiNx film's refractiveindex (real part) and extinction coefficient for the KrF excimer laserbeam were 2.3 and 0.6 respectively. The film thickness and refractiveindex constitute the anti-reflection conditions of the interferencefilm.

This SiNx/Si two-layer film kept the reflectivity of the KrF excimerlaser beam (as the exposure light) for the resist below 0.01% (energyratio), almost below the nonreflective level, irrespective of thelocation (i.e., without being influenced by SOG film thickness orsubstrate steps). Here, the Si film forming chamber and the SiNx filmforming chamber use separate sputtering apparatuses. The use of separatechambers enabled a desired gas mixture ratio to be obtained stably. Itis also possible to form-two kinds of film with a single chamber. Commonuse of the chamber of course lowers equipment cost.

Because in this embodiment the film is a sputtered film formed in theatmosphere of N₂ and Ar gases, the film does not contain a substance,such as ammonia, that reacts with a chemically amplified resistutilizing an acid catalyst reaction. As reported in the Proceedings ofSPIE, 1994, vol. 2195, pp. 422-446, the film was found to have acharacteristic that resist pattern geometry flaws (footing orundercutting) were not likely to occur at the substrate interface.

Next, as shown in FIG. 21(c), a resist 316 was applied over the SiNxfilm 315. The resist's refractive index (real part) and extinctioncoefficient for the KrF excimer laser beam were 1.8 and 0.02respectively. Then, as shown in FIG. 21(d), exposure light 318 wasradiated against the resist 316 through a mask 317 in a conventionalway. A KrF excimer laser beam was used as the exposure light. Though notshown, this exposure used a stepper with a lens numerical aperture of0.45. This is only one example of experimental conditions, and aproximity exposure method may be used instead.

Next, as shown in FIG. 21(e), the resist was developed in an ordinaryway to form a resist pattern 316 a. Then, as shown in FIG. 21(f), withthe resist pattern 316 a as a mask, the SiNx anti-reflective film 315and the silicon film 314 were etched to form over the substrate a resistpattern 319 including a processed anti-reflective film. Because theetched film thickness is as thin as 0.05 μm even where the two films—SiNx anti-reflective film 315 and Si film 314—are combined, nodimensional shift was observed during the etching.

This anti-reflection method was used to form a 0.25-μm pattern, whosedimensional accuracy was found to be 5%. When a conventionalanti-reflective film with 0.05-μm thickness was used, the dimensionalaccuracy could not be improved from 10% no matter how much thephotoabsorption coefficient was optimized.

The pattern detection for alignment was done through thisanti-reflective film, and a sufficient pattern detection signal wasobtained. This is because the anti-reflective film exhibits a sufficientlight shielding capability for the KrF excimer laser beam but has atransmittivity of 95% or more for light whose wavelength is longer than540 nm, the wavelength of the pattern detection beam. This is one of thefeatures offered by the SiNx/Si two-layer anti-reflective film.

Although we described a case of 0.025-μm thickness, the Si filmthickness can be at least this value (i.e., it can be greater than thisvalue). As is evident from FIG. 22, which shows the change ofreflectivity of the SiNx film with the film thickness, it is possible toproduce a reflection prevention effect greater than that of theconventional anti-reflective film by controlling the thickness of theSiNx film in the 0.017-to-0.039 μm range.

Embodiment 17

A seventeenth embodiment of this invention is described by referring toFIGS. 23(a)-(f). First, as shown in FIG. 23(a), a silicon wafer 331 as asubstrate with steps was deposited with an aluminum film 332 (containing2% silicon) to a thickness of 0.3 μm and further with a PSG(phospho-silicate glass) film 333. The thickness of the PSG film variedfrom one location to another due to the steps of the substrate, rangingfrom 0.3 μm to 0.6 μm. The PSG film is transparent to a KrF excimerlaser beam.

Next, as shown in FIG. 23(b), an SiOxNyHz film 334 was deposited overthe PSG film to a thickness of 0.025 μm by a plasma CVD method. Theforming of this SiOxNyHz film used a gas mixture of silane and nitrousoxide, and its mixture ratio was set so that the film's extinctioncoefficient for the KrF excimer laser beam would be 1.8. The film'srefractive index (real part) was 2.2. The gas mixture had a volume ratioof silane (SiH₄) to nitrous oxide (N₂O), SiH₄/N₂O=2.7. This filmreflects more than 90% (energy ratio) of the KrF excimer laser beam. TheSiOxNyHz film as the reflective film exhibited good reflectioncharacteristic also when its thickness was greater than that of thisexample.

After this, an SiOxNyHz film 335 was deposited over the reflective film334 to a thickness of 0.027 μm, by a plasma CVD method. The forming ofthe SiOxNyHz film used a gas mixture of silane and nitrous oxide as withthe film 334, but at a mixture ratio such that the extinctioncoefficient for the KrF excimer laser beam would be 0.7. The refractiveindex (real part) at this time was 2.1. The mixture ratio ofSiH₄/N₂O=1.5. Because this is a CVD film, the film can be deposited to auniform thickness despite there being steps on the substrate, and thushas high film thickness controllability. This is an advantage of the CVDmethod.

This two-layer film consisting of the films 334 and 335 kept thereflectivity of the KrF excimer laser beam for the resist below 0.02%(energy ratio), almost below the nonreflective level, irrespective ofthe location.

Next, as shown in FIG. 23(c), a resist 336 was deposited over theSiOxNyHz film 335. The resist's refractive index and extinctioncoefficient for the KrF excimer laser beam were 1.8 and 0.02respectively. Then, as shown in FIG. 23(d), exposure light 338 wasradiated against the resist 336 through a mask 337 in a conventionalway. A KrF excimer laser beam was used for the exposure light. Thoughnot shown, this exposure used a stepper with a lens numerical apertureof 0.45. This is only one example of experimental conditions, and aproximity exposure method may be used instead.

Then, as shown in FIG. 23(e), the resist 336 was developed according toa conventional procedure to form a resist pattern 336 a. Then, as shownin FIG. 23(f), with the resist pattern 336 a as a mask, the SiOxNyHzanti-reflective films 334, 335 were etched to form over the substrate aresist pattern 339 including processed anti-reflective films.

This anti-reflection method was used to form a 0.25-μm pattern, whosedimensional accuracy was found to be 5%. When a conventional CVD typeanti-reflective film with 0.052-μm thickness was used, the dimensionalaccuracy could not be improved from 10% no matter how much thephotoabsorption coefficient was optimized. Depositing an SiO₂ or SiNxfilm over the CVD film 335 to a thickness of several nm by sputteringprevents anomalies of a chemically amplified resist geometry at theinterface with the substrate, as in the case of Embodiment 16.

Embodiment 18

An embodiment of this invention is described by referring to FIGS.24(a)-(g). First, as shown in FIG. 24(a), a silicon wafer 341 wasdeposited with an oxide film 342 (gate oxide film) to a thickness of 4.5nm, and further with a tungsten film 343 to a thickness of 0.2 μm. Onthe top of the tungsten film was formed an HLD (high temperature lowpressure decomposition) film 344 to a thickness of 0.2 μm. Then, asshown in FIG. 24(b), the HLD film 344 was coated with a tungsten film345 (reflective film) to a thickness of 0.02 μm. This film's refractiveindex and extinction coefficient for a KrF excimer laser beam were 3.40and 2.85 respectively. This film reflects more than 94% (energy ratio)of the KrF excimer laser beam. The tungsten film as the reflective filmexhibited good reflection characteristics also when its thickness wasgreater than that of this example.

After this, an SiNx film (interference anti-reflective film) 346 wasdeposited over the tungsten film 345 to a thickness of 0.028 μm by an RFsputtering method, with Si as a target and N₂ and Ar gases asatmosphere. The gas mixture ratio was adjusted so that the SiNx film'srefractive index (real part) and extinction coefficient for the KrFexcimer laser beam were 2.3 and 0.6 respectively. Then, a resist 347 wasapplied over the SiNx film 346. The resist's refractive index (realpart) and extinction coefficient for the KrF excimer laser beam were 1.8and 0.02 respectively.

Next, as shown in FIG. 24(c), exposure light 349 was radiated againstthe resist 347 through a mask 348 in a conventional manner. An KrFexcimer laser beam was used for the exposure light. Though not shown,this exposure used a stepper with a lens numerical aperture of 0.45.This is only one example of experimental conditions, and a proximityexposure method may be used instead.

Next, as shown in FIG. 24(d), the resist 347 was developed in a knownway to form a resist pattern 347 a. Then, as shown in FIG. 24(e), withthe resist pattern 347 a as a mask, the SiNx anti-reflective film 346,the tungsten anti-reflective film 345 and the HLD film 344 were etchedto form a pattern 3410 consisting of SiNx, tungsten reflective film andHLD. The etching rate at this time was 3 for SiNx, 1.3 for the tungstenreflective film, and 3 for the HLD film, compared with 1 for resist.

Then, as shown in FIG. 24(f), the resist pattern 347 a was removed in anormal way. After this, as shown in FIG. 24(g), with the pattern 3410consisting of SiNx, W reflective film and HLD as a mask, the tungstenfilm 343 was etched by using an SF₆ gas to form a gate interconnectpattern 343 a. The ratio of etching rates at this time was 1:1.2:1tungsten film, SiNx and HLD film. Hence, the thin tungsten reflectivefilm and SiNx interference anti-reflective film were removedsimultaneously with this etching. The etching apparatus used a microwaveetching apparatus. This, however, is only one experimental condition,and other etching conditions may be used. While we used an SF₆ gas forthe etching gas, other etching gases, such as CF₄ and NF₃, may also beused.

The ability to remove this anti-reflective film without requiring aspecial removing process is one of the features of this method. Thisfeature can be obtained not only when a tungsten gate interconnect filmis used, but also when a tungsten silicide film, a tungsten polycidefilm or a stack of these films including polysilicon is used. Thisanti-reflection method was used to form a 0.25-μm-wide gate interconnectpattern, and its dimensional accuracy was found to be 5%. When aconventional anti-reflective film with 0.05-μm thickness was used, thedimensional accuracy could not be improved from 10% no matter how muchthe absorption coefficient was optimized.

Embodiment 19

A wafer with steps having gates formed thereon was deposited with an SOGfilm (interlayer insulating film and planarized film) to a thickness of0.3 μm and further with an aluminum film (containing 2% silicon) to athickness of 0.4 μm. On top of it, an HLD (high temperature low pressuredecomposition) film was formed to a thickness of 0.2 μm. After this, theHLD film was coated with an aluminum film (reflective film) to athickness of 0.04 μm. The aluminum film's refractive index (real part)and extinction coefficient for a KrF excimer laser beam were 0.19 and2.94 respectively. This film reflects more than 99% (energy ratio) ofthe KrF excimer laser beam. The aluminum film as the reflective filmexhibited good reflection characteristics for greater thicknesses, also.

Then, an SiOxNyHz film was deposited over this aluminum film to athickness of 0.019 μm by a plasma CVD method. The forming of theSiOxNyHz film used a gas mixture of silane and nitrous oxide. The gasmixture ratio was set so that the film's extinction coefficient for theKrF excimer laser beam would be 0.9. The refractive index (real part) atthis time was 2.48. Because this is a CVD film, the film can bedeposited to a uniform thickness despite there being steps on thesubstrate, and thus has high film thickness controllability. This is anadvantage of the CVD method.

After this, a resist was applied over the SiOxNyHz film. The resist'srefractive index (real part) and extinction coefficient for the KrFexcimer laser beam were 1.8 and 0.02 respectively. Next, the resist wasirradiated with exposure light through a mask in a conventional way. AnKrF excimer laser beam was used for the exposure light. This exposureused a stepper with a lens numerical aperture of 0.45. This is only oneexample of experimental conditions, and a proximity exposure method maybe used instead. The resist was then developed in a conventional way toform a resist pattern.

Then, with the resist pattern as a mask, the SiOxNyHz anti-reflectivefilm, the aluminum reflective film and the HLD film were etched to forma pattern consisting of SiOxNyHz, aluminum and HLD. After this, theresist pattern was removed according to a known procedure. This wasfollowed by the 0.4-μm thick aluminum film being etched, with thepattern of SiOxNyHz, aluminum and HLD used as a mask, to form analuminum interconnect pattern. At this time, the thin aluminumanti-reflective film and SiOxNyHz interference anti-reflective film wereremoved simultaneously with this etching. The ability to remove thisanti-reflective film without requiring a special removing process is oneof the features of this method.

These reflection prevention effects can be obtained not only when thealuminum gate interconnect film is used, but also when a Ti film, Tafilm or Pt film is used. This anti-reflection method was used to form a0.25-μm-wide interconnect pattern and its dimensional accuracy was foundto be 5%. When a conventional anti-reflective film with 0.05-μmthickness was used, the dimensional accuracy could not be improved from10% no matter how much the photoabsorption coefficient was optimized.

Embodiment 20

A silicon wafer as a substrate with steps was deposited with an aluminumfilm to a thickness of 0.2 μm, as in the case of Embodiment 16, andfurther with an SOG (spin on glass) film. The thickness of the SOG filmvaried according to location due to the steps of the substrate, rangingfrom 0.2 μm to 0.5 μm. The SOG film was transparent to a KrF exciterlaser beam (wave length 248 nm). Next, the SOG film was coated with analuminum film (reflective film) to a thickness of 0.041 μm. The aluminumfilm's refractive index (real part) and extinction coefficient for theKrF excimer laser beam were 0.19 and 2.94 respectively. Then, thisaluminum film was deposited with an SiNx film (interferenceanti-reflective film) to a thickness of 0.019 μm by a DC sputteringmethod, with silicon as a target and N₂ and Ar gases as atmosphere.Here, the gas mixture ratio was adjusted so that the SiNx film'srefractive index (real part) and extinction coefficient for the KrFexcimer laser beam would be 2.48 and 0.9 respectively. The filmthickness and the refractive index constitute the reflection preventioncondition for the interference film.

This SiNx/Al two-layer film kept the reflectivity of the KrF excimerlaser beam (as the exposure light) for the resist below 0.01% (energyratio), almost below the nonreflective level, irrespective of thelocation (i.e., without being influenced by the SOG film thickness orthe steps of the substrate). Next, a resist was deposited over the SiNxfilm. The resist's refractive index (real part) and extinctioncoefficient for the KrF excimer beam were 1.8 and 0.02 respectively.Then, exposure light was radiated against the resist through a mask in aconventional way. A KrF excimer laser beam was used for the exposurelight. This exposure used a stepper with a lens numerical aperture of0.45. This is only one example of experimental conditions, and aproximity exposure method may be used instead.

Then, the resist was developed according to a conventional procedure toform a resist pattern. Then, with the resist pattern as a mask, the SiNxanti-reflective film and the aluminum film were etched to form over thesubstrate a resist pattern including a processed anti-reflective film.This anti-reflection method was used to form a 0.25-μm pattern, whosedimensional accuracy was found to be 5%. On the other hand, as isevident from FIG. 25, which shows the change of reflectivity of thealuminum film with the film thickness, it is possible to produce asufficient reflection prevention effect when the aluminum film thicknessis equal to or greater than 0.04 μm.

When a conventional anti-reflective film with 0.06-μm thickness wasused, the dimensional accuracy could not be improved from 10% no matterhow much the photoabsorption coefficient was optimized. Pt was able tobe used instead of the aluminum reflective film.

Embodiment 21

A silicon wafer as a substrate with steps was deposited with a tungstenfilm (containing 2% silicon) to a thickness of 0.3 μm, as in the case ofEmbodiment 16, and further with a PSG (phosphosilicate glass) film. Thethickness of the PSG film varied according to location due to the stepsof the substrate, ranging from 0.3 μm to 0.6 μm. The PSG film wastransparent to a KrF excimer laser beam. Next, the PSG film was coatedwith a tungsten film to a thickness of 0.02 μm. The tungsten film'srefractive index (real part) and extinction coefficient for the KrFexcimer laser beam were 3.4 and 2.85 respectively. The reflectivity ofthis film for the KrF excimer beam was more than 94% (energy ratio).

Then, this tungsten film was deposited with an SiOxNyHz film to athickness of 0.034 μm by a plasma CVD method. The forming of theSiOxNyHz film used a gas mixture of silane and nitrous oxide with amixture ratio so set that the film's extinction coefficient would be0.6. The refractive index (real part) at this time was 2.08. Becausethis is a CVD film, the film can be deposited to a uniform thicknessdespite there being steps on the substrate, and thus has high filmthickness controllability. This is an advantage of the CVD method. ThisSiOxNyHz/W two-layer film kept the reflectivity of the KrF excimer laserbeam for the resist below 0.01% (energy ratio), almost below thenonreflective level, irrespective of the location.

Next, a resist was deposited over the SiOxNyHz film. The resist'srefractive index and extinction coefficient for the KrF excimer laserbeam were 1.8 and 0.02 respectively. Then, exposure light was radiatedagainst the resist through a mask in a conventional way. A KrF excimerlaser beam was used for the exposure light. This exposure used a stepperwith a lens numerical aperture of 0.45. This is only one example ofexperimental conditions, and a proximity exposure method may be usedinstead.

Then, the resist was developed according to a conventional procedure toform a resist pattern. Then, with the resist pattern as a mask, theSiOxNyHz anti-reflective film was etched to form over the substrate aresist pattern including a processed anti-reflective film. Thisanti-reflection method was used to form a 0.25-μm pattern, whosedimensional accuracy was found to be 5%. On the other hand, when aconventional CVD type anti-reflective film with 0.054-μm thickness wasused, the dimensional accuracy could not be improved from 10% no matterhow much the photoabsorption coefficient was optimized.

Embodiment 22

A silicon wafer as a substrate with steps was deposited with a tungstenfilm to a thickness of 0.2 μm, as in the case of Embodiment 16, andfurther with an SOG (spin on glass) film. The thickness of the SOG filmvaried according to location due to the steps of the substrate, rangingfrom 0.2 μm to 0.5 μm. The SOG film was transparent to i line radiation(wavelength 365 nm). Next, the SOG film was coated with a silicon film(reflective film) to a thickness of 0.025 μm by a DC sputtering method,with Si as a target and Ar gas as atmosphere. The silicon film'srefractive index (real part) and extinction coefficient for i lineradiation were 4.6 and 2.7 respectively. The reflectivity of this filmfor i line radiation was more than 95% (energy ratio).

Then, this silicon film was deposited with an SiNx film (interferenceanti-reflective film) to a thickness of 0.029 μm by a DC sputteringmethod, with Si as a target and N₂ and Ar gases as atmosphere. The gasmixture ratio was adjusted so that the SiNx film's refractive index(real part) and extinction coefficient for i line radiation were 2.8 and0.4 respectively. The film thickness and the refractive index constitutethe reflection prevention conditions for the interference film. ThisSiNx/Si two-layer film kept the reflectivity of i line radiation for theresist below 0.2% is (energy ratio), almost below the nonreflectivelevel, irrespective of the location (i.e., without being influenced bythe SOG film thickness or the steps of the substrate).

Next, a resist was deposited over the SiNx film. The resist's refractiveindex and extinction coefficient for i line radiation were 1.7 and 0.00respectively. Then, exposure light was radiated against the resistthrough a mask in a conventional way. The i line radiation was used forthe exposure light. Then, the resist was developed in a conventional wayto form a resist pattern.

After this, with the resist pattern as a mask, the SiNx anti-reflectivefilm and the Si film were etched to form over the substrate a resistpattern including a processed anti-reflective film. This anti-reflectionmethod was used to form a 0.35-μm pattern, whose dimensional accuracywas found to be 5%. On the other hand, when a conventionalanti-reflective film with 0.05-μm thickness was used, the dimensionalaccuracy could not be improved from 15% no matter how much thephotoabsorption coefficient was optimized. Although the case of 0.029-μmthickness was described here, if the SiNx film thickness could beincreased to 0.1 μm, the reflectivity was able to be further reduced to0.1 by setting the refractive index to 2.6 and the extinctioncoefficient to 0.2.

Embodiment 23

A twenty-third embodiment of this invention is described by referring toFIGS. 26(a)-(e). First, the substrate is deposited with an organic film352 and heat-treated at 150° C., as shown in FIG. 26(a). The filmthickness was set to 0.15 μm over a planar surface. In areas where thefilm was thin due to steps on the substrate surface, the film thicknesswas 0.08 μm. In thick areas, it was 0.23 μm. Methylmethacrylate-9-Anthylmethylmethacrylate copolymer was used as theorganic film 352. The polymer has a bleaching characteristic. As asubstrate, a silicon wafer 350 having steps and deposited with tungsten351 to a thickness of 0.2 μm was used.

Next, as shown in FIG. 26(b), a resist 353 was spun onto the organicfilm 352 in a conventional manner, and was baked.

Then as shown in FIG. 26(c), exposure light 356 was applied to theresist 353 through a mask 355, according to a known procedure. A KrFexcimer laser beam was used for the exposure light. While the mask isshown close to the film, it is possible to perform exposure through alens or mirror.

The pattern exposure light reached the organic film 352, the uppersurface side of the organic film 352 was bleached, and a relativelyhighly transparent layer 354 to the exposure light was formed in theupper surface of the organic film. By the process, an anti-reflectivefilm whose exposure light absorbance is greater on the substrate surfaceside than on the resist surface side is formed automatically.

Next, as shown in FIG. 26(d), the resist 353 was developed to form aresist pattern 353. Then, as shown in FIG. 26(e), with the resistpattern 353 a as a mask, the organic film (anti-reflective film) wasetched to form over the substrate a resist pattern 357 including aprocessed anti-reflective film. This anti-reflective method was used toform a 0.25 μm pattern, whose dimensional accuracy was found to be 5%.When a commercially available ARC type anti-reflective film with 0.15-μmthickness was used, the dimensional accuracy was 8%. Increasing the filmthickness of ARC posed a problem of dimensional shift and collapse ofthe resist pattern during etching.

This method makes it possible to automatically form the photoabsorbancedistribution in an anti-reflective film without any additionalprocedure. Therefore, this method is simple and is effective to reducethe cost. This is an advantage of this method.

A very high reflection prevention effect can be produced for a varietyof kinds of substrates, including those having transparent films andthose having high reflectivity like metallic films, without posing anyproblem, such as aspect ratios, during the process of forminganti-reflective films. This method can form fine and precise resistpatterns and therefore improve the yield and reliability of devices tobe manufactured. When applied to logic LSIs, this invention enables themto be manufactured at high dimensional precision and increases theiroperation speeds.

While we have shown and described several embodiments in accordance withthe present invention, it is understood that the same is not limitedthereto, but is susceptible to numerous changes and modifications as isknown in the art; and we therefore do not wish to be limited to thedetails shown and described herein, but intend to cover all suchmodifications as are encompassed by the scope of the appended claims.

What is claimed is:
 1. A method of manufacturing a semiconductor device,comprising: providing a body which has a metal film, a spin-on-glassfilm, a first film, a second film, and a resist film which has a patternformed by using an exposure light; etching the second film and the firstfilm by using the resist film as an etching mask; and removing theresist film, wherein the second film has a smaller extinctioncoefficient for the exposure light than that of the first film.
 2. Amethod of manufacturing a semiconductor device according to claim 1,wherein the exposure light is a laser beam.
 3. A method of manufacturinga semiconductor device according to claim 1, wherein the body has steps,the metal film having the steps.
 4. A method of manufacturing asemiconductor device according to claim 1, wherein the first film andthe second film are multiple layers of an anti-reflective film.
 5. Amethod of manufacturing a semiconductor device according to claim 1,wherein the spin-on-glass film is a transparent film for the exposurelight.
 6. A method of manufacturing a semiconductor device according toclaim 1, wherein the metal film, spin-on-glass film, first film, secondfilm and resist film are in order, with the resist film as the uppermostfilm, as a laminate of films.
 7. A method of manufacturing asemiconductor device according to claim 6, wherein the laminate of filmsis provided on a substrate.
 8. A method of manufacturing a semiconductordevice, comprising: providing a substrate with steps; forming a metalfilm, an insulating film, a first film, a second film, and a resistfilm, in order, on the substrate; exposing the resist film so as to makea resist pattern by using an exposure light; etching the second film andthe first film by using the resist film as an etching mask; and removingthe resist film, wherein the second film has a smaller extinctioncoefficient for the exposure light than that of the first film.
 9. Amethod of manufacturing a semiconductor device according to claim 8,wherein the first film and the second film are multiple layers of ananti-reflective film.
 10. A method of manufacturing a semiconductordevice according to claim 8, wherein the insulating film is atransparent film for the exposure light.